explorations and thoughts about the natural world

Hierarchy Shift

Brown bears live in a hierarchy, where dominance allows greater access to food and the most productive fishing areas. One recent interaction between bears 32 Chunk and 480 Otis represents a shift in this social order. This is a story of maturation for two bears going in opposite hierarchical directions.

The hierarchy at Brooks River allows bears to quickly assess their competitors, avoiding most physical fights and saving valuable energy. Within the hierarchy large, mature males rank highest followed by other adult males, females with cubs, single females, and finally subadult bears. While this pattern holds as a general rule, bears shift their position in the hierarchy depending on their size, strength, and overall health.

As an adult male in his early teens, 32 Chunk is well positioned to rank near the top of the hierarchy. Chunk was first identified in 2007 as a chunky subadult bear. We don’t know his exact age, but bear monitoring staff noted he appeared to be a young subadult, perhaps 3.5 or 4.5 years old at the time. Since then, he’s grown considerably and is among the largest bears at Brooks River.

32 Chunk as a young subadult in 2007. Ten years later, he has grown to become one of the largest bears at Brooks River. (Photo courtesy of Jeanne Roy.)

In contrast, 480 Otis was a mature adult in his early teens in 2007. He was a big, walrus-shaped bear who, like today, was skilled at fishing in the jacuzzi and far pool. He was not often displaced from his preferred fishing spots.

480 Otis in 2007. (NPS Photo)

In 2007 and 2008, a young subadult bear like Chunk wouldn’t even consider challenging a larger adult like Otis. Since then both bears have matured, but their life histories since then lead in different directions within the hierarchy. Recently, 32 Chunk demonstrated his dominance over the older 480 Otis.

When the video begins, 480 Otis is standing upstream of the falls in the middle of the river. 32 Chunk is the darker colored bear in the jacuzzi below the falls.

After Chunk notices Otis above the falls, he leaves the jacuzzi and begins to approach Otis.

480 Otis starts to move away, possibly to avoid 32 Chunk’s approach. This is one sign Otis could be subordinate to 32. The rest of the interaction leaves no doubt who is dominant, however.

Chunk moves through the river faster than Otis. When Chunk nears the older bear, Otis turns to face the younger competitor. They stand mostly still, yawning and assessing each other’s size.

32 Chunk then swats at 480 Otis.

In the video, the bears’ ear positions aren’t easy to see, but 480’s ears seem to be held back against his head, indicating he’s somewhat defensive. Chunk’s ears, in contrast, are mostly upright and oriented forward, a sign of assertiveness and dominance in this context.

32’s ears were upright and forward, while 480’s ears were held slightly back against his head.

32 ended the encounter, turning his back on 480 and walking away. (Dominant bears decide when an interaction ends unless they have good reason to usurp a resource such as food, a fishing spot, or access to a potential mate.)

Chunk is now entering the prime of his life where he’ll attain his greatest size and rank, and while Otis remains a large bear he’s no longer able to compete with the largest male bears for fishing spots. It seems that Chunk recognizes his size and strength and Otis recognizes the great risks of challenging a younger, larger bear. For the rest of the summer, 32 may displace 480 from fishing spots at Brooks Falls.

Chunk appears to be moving up the hierarchy while Otis continues to slide down it. With these bears, there are two tales of maturation.

9 thoughts on “Hierarchy Shift”

great discription Mike, iam very courious, whether we can see what happens when 32 Chunk meets 856 and 747 , it look like that 634 popeye accept 32s dominace https://youtu.be/IalVpWr8ypQ?t=9m58s
iam wondering about that 856 not showed up at BF very often and 747 not had seen so far at BF because of 32 Chunk??

Thanks for the link. 32 Chunk has definitely grown quite a bit over the past few years, and looks impressively large. In the video, he appears to directly approach the area where 634 was standing and 634 appears to avoid him by moving away. Based on those observations, 32 is probably more dominant than 634.

I am also curious to see 32 interact with 747 and 856. These bears are the largest of the largest on the river. 856 can’t stay at the top of the hierarchy forever. Each year, dominant bears face new challengers. Eventually one challenger will become large enough and strong enough to displace him.

Mike, from what you’ve seen, is 32 Chunk larger now in his prime, than 480 Otis was 10 years ago when he was in his prime? Back in 2007 when 480 was higher up in the hierarchy than he is today, was he an aggressive bear that would push his position and engage with other bears? Or would he rather just use his large body mass to intimidate and push lower ranking bears out of his preferred fishing spots? Do you believe that aggressive behavior in more dominant males is a learned trait, instinct or hereditary?

From what I remember, Chunk is at least as big as Otis was. In 20007 and 2008, when Otis ranked higher in the hierarchy, I don’t recall him acting aggressively towards other bears. He knew he was big though, and would shoulder smaller bears, like 747, out of the jacuzzi. He’d walk up behind them and if they didn’t leave, he’d inch closer and closer, often growling at the same time.

To answer your last question, I must speculate because I haven’t read any studies which might explain the behavior. Is disposition, particularly aggressiveness, a product of nature, nuture, or both? I believe aggressiveness, to the level of hyperdominant bears like 856 take it, is probably influenced by a combination of genes and learned behavior. 856 likely has learned he can intimidate certain bears more than others, but he also was born with the instincts to carry those behaviors out. Not all bears behave like 856, even though they posses great size. 747, for instance, is very dominant but is less likely to start an altercation than 856 from what I’ve observed.

So glad to hear all of this information, Mike. Makes bear viewing so much more enjoyable. Also, your
answers to readers questions add another layer of knowledge. I wondered when I saw that Otis had moved out of “his” office if a hierarchy shift was afoot. Didn’t connect the dots to Chunks assertive behavior until I read your blog. Thank you.